From the ancient origins link above:

While the author Wade Davis admits the story could be “apocryphal”, he cited the autobiography of Peter Freuchen who claimed to have shaped his own feces into a frozen chisel to make his escape.

So he claimed he did it himself as well as saying he knew how to do it because of the “well known account”. But also, anthropologists made shit up about the cultures they studied all the time, which is what I was actually referring to.